Add tpm2.PolicySigned; fix PolicySecret signature

Add the ability to call TPM2_PolicySigned, and add PolicySigned
test to verify correct behavior given different expiration values.

Change TPM2_PolicySecret's signature to add the timeout, as described in Part
3 of the spec.

tpm2/constants.go

@@ -400,7 +400,9 @@ const (
 	TagAttestCertify  tpmutil.Tag = 0x8017
 	TagAttestQuote    tpmutil.Tag = 0x8018
 	TagAttestCreation tpmutil.Tag = 0x801a
+	TagAuthSecret     tpmutil.Tag = 0x8023
 	TagHashCheck      tpmutil.Tag = 0x8024
+	TagAuthSigned     tpmutil.Tag = 0x8025
 )
 
 // StartupType instructs the TPM on how to handle its state during Shutdown or
@@ -470,6 +472,7 @@ const (
 	CmdSequenceUpdate             tpmutil.Command = 0x0000015C
 	CmdSign                       tpmutil.Command = 0x0000015D
 	CmdUnseal                     tpmutil.Command = 0x0000015E
+	CmdPolicySigned               tpmutil.Command = 0x00000160
 	CmdContextLoad                tpmutil.Command = 0x00000161
 	CmdContextSave                tpmutil.Command = 0x00000162
 	CmdECDHKeyGen                 tpmutil.Command = 0x00000163

tpm2/test/tpm2_test.go

@@ -79,8 +79,32 @@ var (
 			ExponentRaw: 1<<16 + 1,
 		},
 	}
-	defaultPassword = "\x01\x02\x03\x04"
-	emptyPassword   = ""
+	defaultPassword        = "\x01\x02\x03\x04"
+	emptyPassword          = ""
+	defaultRsaSignerParams = Public{
+		Type:       AlgRSA,
+		NameAlg:    AlgSHA256,
+		Attributes: FlagSign | FlagSensitiveDataOrigin | FlagUserWithAuth,
+		RSAParameters: &RSAParams{
+			Sign: &SigScheme{
+				Alg:  AlgRSASSA,
+				Hash: AlgSHA256,
+			},
+			KeyBits: 2048,
+		},
+	}
+	defaultEccSignerParams = Public{
+		Type:       AlgECC,
+		NameAlg:    AlgSHA256,
+		Attributes: FlagSign | FlagSensitiveDataOrigin | FlagUserWithAuth,
+		ECCParameters: &ECCParams{
+			Sign: &SigScheme{
+				Alg:  AlgECDSA,
+				Hash: AlgSHA256,
+			},
+			CurveID: CurveNISTP256,
+		},
+	}
 )
 
 func min(a, b int) int {
@@ -1494,15 +1518,87 @@ func TestPolicySecret(t *testing.T) {
 	rw := openTPM(t)
 	defer rw.Close()
 
+	_, _ = testPolicySecret(t, rw, 0)
+}
+
+func testPolicySecret(t *testing.T, rw io.ReadWriter, expiration int32) ([]byte, *Ticket) {
 	sessHandle, _, err := StartAuthSession(rw, HandleNull, HandleNull, make([]byte, 16), nil, SessionPolicy, AlgNull, AlgSHA256)
 	if err != nil {
 		t.Fatalf("StartAuthSession() failed: %v", err)
 	}
 	defer FlushContext(rw, sessHandle)
 
-	if _, err := PolicySecret(rw, HandleEndorsement, AuthCommand{Session: HandlePasswordSession, Attributes: AttrContinueSession}, sessHandle, nil, nil, nil, 0); err != nil {
+	timeout, tkt, err := PolicySecret(rw, HandleEndorsement, AuthCommand{Session: HandlePasswordSession, Attributes: AttrContinueSession}, sessHandle, nil, nil, nil, expiration)
+	if err != nil {
 		t.Fatalf("PolicySecret() failed: %v", err)
 	}
+	return timeout, tkt
+}
+
+func TestPolicySigned(t *testing.T) {
+	rw := openTPM(t)
+	defer rw.Close()
+
+	var nullTicket = Ticket{Type: TagAuthSigned, Hierarchy: HandleNull}
+	signers := map[string]Public{
+		"RSA": defaultRsaSignerParams,
+		"ECC": defaultEccSignerParams,
+	}
+
+	expirations := []int32{math.MinInt32, math.MinInt32 + 1, -1, 0, 1, math.MaxInt32}
+	for _, expiration := range expirations {
+		for signerType, params := range signers {
+			t.Run(t.Name()+signerType+fmt.Sprint(expiration), func(t *testing.T) {
+				_, tkt := testPolicySigned(t, rw, expiration, params)
+				if expiration < 0 && len(tkt.Digest) == 0 {
+					t.Fatalf("Got empty ticket digest, expected ticket with auth expiry")
+				} else if expiration >= 0 && !reflect.DeepEqual(*tkt, nullTicket) {
+					t.Fatalf("Got ticket with non-empty digest, expected NULL ticket")
+				}
+			})
+		}
+	}
+}
+
+func testPolicySigned(t *testing.T, rw io.ReadWriter, expiration int32, signerParams Public) ([]byte, *Ticket) {
+	handle, _, err := CreatePrimary(rw, HandleOwner, PCRSelection{}, emptyPassword, emptyPassword, signerParams)
+	if err != nil {
+		t.Fatalf("CreatePrimary() failed: %s", err)
+	}
+	defer FlushContext(rw, handle)
+
+	sessHandle, nonce, err := StartAuthSession(rw, HandleNull, HandleNull, make([]byte, 16), nil, SessionPolicy, AlgNull, AlgSHA256)
+	if err != nil {
+		t.Fatalf("StartAuthSession() failed: %v", err)
+	}
+	defer FlushContext(rw, sessHandle)
+
+	// Sign the hash of the command parameters, as described in the TPM 2.0 spec, Part 3, Section 23.3.
+	// We only use expiration here.
+	expBytes := make([]byte, 4)
+	binary.BigEndian.PutUint32(expBytes, uint32(expiration))
+
+	// TPM2.0 spec, Revision 1.38, Part 3 nonce must be present if expiration is non-zero.
+	// aHash ≔ HauthAlg(nonceTPM || expiration || cpHashA || policyRef)
+	toDigest := append(nonce, expBytes...)
+
+	digest := sha256.Sum256(toDigest)
+
+	sig, err := Sign(rw, handle, emptyPassword, digest[:], nil, nil)
+	if err != nil {
+		t.Fatalf("Sign failed: %s", err)
+	}
+
+	signature, err := sig.Encode()
+	if err != nil {
+		t.Fatalf("Encode() failed: %v", err)
+	}
+
+	timeout, tkt, err := PolicySigned(rw, handle, sessHandle, nonce, nil, nil, expiration, signature)
+	if err != nil {
+		t.Fatalf("PolicySigned() failed: %v", err)
+	}
+	return timeout, tkt
 }
 
 func TestQuote(t *testing.T) {

tpm2/tpm2.go

@@ -747,38 +747,71 @@ func encodePolicySecret(entityHandle tpmutil.Handle, entityAuth AuthCommand, pol
 	return concat(handles, auth, params)
 }
 
-func decodePolicySecret(in []byte) (*Ticket, error) {
+func decodePolicySecret(in []byte) ([]byte, *Ticket, error) {
 	buf := bytes.NewBuffer(in)
 
 	var paramSize uint32
 	var timeout tpmutil.U16Bytes
 	if err := tpmutil.UnpackBuf(buf, &paramSize, &timeout); err != nil {
-		return nil, fmt.Errorf("decoding timeout: %v", err)
+		return nil, nil, fmt.Errorf("decoding timeout: %v", err)
 	}
 	var t Ticket
 	if err := tpmutil.UnpackBuf(buf, &t); err != nil {
-		return nil, fmt.Errorf("decoding ticket: %v", err)
+		return nil, nil, fmt.Errorf("decoding ticket: %v", err)
 	}
-	return &t, nil
+	return timeout, &t, nil
 }
 
 // PolicySecret sets a secret authorization requirement on the provided entity.
-// If expiry is non-zero, the authorization is valid for expiry seconds.
-func PolicySecret(rw io.ReadWriter, entityHandle tpmutil.Handle, entityAuth AuthCommand, policyHandle tpmutil.Handle, policyNonce, cpHash, policyRef []byte, expiry int32) (*Ticket, error) {
+func PolicySecret(rw io.ReadWriter, entityHandle tpmutil.Handle, entityAuth AuthCommand, policyHandle tpmutil.Handle, policyNonce, cpHash, policyRef []byte, expiry int32) ([]byte, *Ticket, error) {
 	Cmd, err := encodePolicySecret(entityHandle, entityAuth, policyHandle, policyNonce, cpHash, policyRef, expiry)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 	resp, err := runCommand(rw, TagSessions, CmdPolicySecret, tpmutil.RawBytes(Cmd))
+	if err != nil {
+		return nil, nil, err
+	}
+	return decodePolicySecret(resp)
+}
+
+func encodePolicySigned(validationKeyHandle tpmutil.Handle, policyHandle tpmutil.Handle, policyNonce, cpHash, policyRef tpmutil.U16Bytes, expiry int32, auth []byte) ([]byte, error) {
+	handles, err := tpmutil.Pack(validationKeyHandle, policyHandle)
 	if err != nil {
 		return nil, err
 	}
+	params, err := tpmutil.Pack(policyNonce, cpHash, policyRef, expiry, auth)
+	if err != nil {
+		return nil, err
+	}
+	return concat(handles, params)
+}
+
+func decodePolicySigned(in []byte) ([]byte, *Ticket, error) {
+	buf := bytes.NewBuffer(in)
 
-	// Tickets are only provided if expiry is set.
-	if expiry != 0 {
-		return decodePolicySecret(resp)
+	var timeout tpmutil.U16Bytes
+	if err := tpmutil.UnpackBuf(buf, &timeout); err != nil {
+		return nil, nil, fmt.Errorf("decoding timeout: %v", err)
+	}
+	var t Ticket
+	if err := tpmutil.UnpackBuf(buf, &t); err != nil {
+		return nil, nil, fmt.Errorf("decoding ticket: %v", err)
+	}
+	return timeout, &t, nil
+}
+
+// PolicySigned sets a signed authorization requirement on the provided policy.
+func PolicySigned(rw io.ReadWriter, validationKeyHandle tpmutil.Handle, policyHandle tpmutil.Handle, policyNonce, cpHash, policyRef []byte, expiry int32, signedAuth []byte) ([]byte, *Ticket, error) {
+	Cmd, err := encodePolicySigned(validationKeyHandle, policyHandle, policyNonce, cpHash, policyRef, expiry, signedAuth)
+	if err != nil {
+		return nil, nil, err
+	}
+	resp, err := runCommand(rw, TagNoSessions, CmdPolicySigned, tpmutil.RawBytes(Cmd))
+	if err != nil {
+		return nil, nil, err
 	}
-	return nil, nil
+	return decodePolicySigned(resp)
 }
 
 func encodePolicyPCR(session tpmutil.Handle, expectedDigest tpmutil.U16Bytes, sel PCRSelection) ([]byte, error) {